Intercellular communication between sympathetic and sensory perivascular nerves (PVNs), smooth muscle cells (SMCs) and endothelial cells (ECs) is essential to the regulation of vasomotor tone and the ability to mobilize blood to body tissues in accord with metabolic demand. Critical to this regulation are myoendothelial junctions (MEJs), which exist at holes (fenestrae) in the internal elastic lamina (IEL) and allow communication of electrical and chemical signals between ECs and SMCs. By releasing neurotransmitters that activate SMCs, PVNs play an important role in the initiating cell-cell communication through MEJs. Advancing age is linked to endothelial dysfunction and impaired exercise capacity, but the underlying changes in signaling mechanisms are still unclear. The majority of studies on intercellular communication do not incorporate the role of PVN, instead focusing on EC-to-SMC communication (e.g., endothelium-dependent hyperpolarization) and how signals originating in ECs affect SMC Ca2+. Therefore, the purpose of this proposal is to characterize EC Ca2+ signals arising from PVN activation of SMCs. In Young (3-4 month) and Old (24-26 month) mice, this project is focused on how stimulation of sympathetic and sensory nerves affects local EC Ca2+ signaling via MEJs. My preliminary studies show aging to be associated with a decrease in the ability of sensory nerves to inhibit sympathetic vasoconstriction along with desensitization of 1-adrenoreceptors. In light of reports linking adrenoreceptor activation to global EC Ca2+ signaling, my data led to the overall hypothesis that local EC Ca2+ signals arising from PVN activation of SMC are altered with aging. To investigate these functional relationships in vivo, I have developed a novel intravital preparation to study mesenteric arteries (MA) in anesthetized transgenic GCaMP2. These animals are bred in house and express an EC-specific Ca2+ indicator (GCaMP2), enabling high speed confocal imaging of local EC Ca2+ in vivo without the need for external dyes or concern for their potential artifacts. Using this model to stimulate PVNs before and during selective inhibition of sensory or sympathetic neurotransmission will address the following Specific Aims: (1) Determine how PVN activation modulates EC Ca2+ signals during blood flow control; and (2) Determine the impact of aging on EC Ca2+ signals and vasomotor function in vivo. Completion of the proposed studies will provide valuable new insight with respect to the role of EC Ca2+ signaling during blood flow control in the young and aging vasculature that may serve as the basis for novel therapeutic strategies for treating age-related endothelial dysfunction.